Polypeptide compounds containing the 3,4-dehydroproline, particularly the L-3,4-dehydroproline residue have been found to be potent inhibitors of proline hydroxylase enzyme activity and thus 3,4-dehydroproline serves as a useful agent for the inhibition of collagen synthesis. Studies with radiolabelled D,L-3,4-dehydroproline is incorporated into collagen and total protein at one-fifth the rate observed for labelled L-3,4-dehydroproline. Moreover, it has been found that D-3,4-dehydroproline does not inhibit hydroxyproline formation while L-3,4-dehydroproline when added to a cell culture in an amount of 1 mM reduced intracellular [.sup.14 C]-hydroxyproline 40% and medium [.sup.14 C]-hydroxyproline 70%. It is clear from the foregoing that the L-antipode of 3,4-dehydroproline would be the therapeutic agent of choice for collagen inhibition. Thus a process for resolving D,L-3,4-dehydroproline to produce L-3,4-dehydroproline in high optical purity and yield would be of great importance.
Resolution of D,L-3,4-dehydroprolinamide has been achieved in the art using both enzymatic and chemical techniques. The enzymatic procedure involved use of hog kidney amidase and produced L-3,4-dehydroproline which contains at least 3% of the D isomer as determined by the manometric assay with D-amino acid oxidase. Attempts to obtain optically pure L-3,4-dehydroproline by fractional crystallization or by enzymatic destruction of the contaminating D-form failed. See Robertson and Witkop, J. Amer. Chem. Soc. 84, 1697 (1962).
These same researchers also resolved D,L-3,4-dehydroprolinamide chemically using ammonium (+)-alpha-bromocamphor-pi-sulfonate. However, the yield of the L-isomer obtained was poor and the optical purity of the product was variable and thus this procedure is not practical from a commercial viewpoint.